Whatever the cast shape, several problems arise in continuous casting due to the incomplete solidity of the cast product during its manufacture. Such problems include warping of the product and diagonal distortion of its cross-sectional shape. Aside from the obvious disadvantages of warping and distortion relating to misshaping, such conditions can cause internal cracking of the cast product. Such cracking, often called "Z cracks" too often results in rejection of the product, at least for its primary use, for failure to meet quality control standards, due to lack of internal product integrity.
Accordingly, some have proposed techniques for monitoring characteristics of a continuously cast product. In one such proposal, a wheel resiliently impinges upon a flat surface of a cast product as it leaves the casting mold. A lever structure responds to fluctuations in the position of the wheel to adjust water spray apparatus to minimize warp in the cast billet. Such a technique, however, senses only warp or waver in the single surface along which the wheel rolls, and cannot with certainty sense directly changes in cross-section of the billet. The system is likely to spuriously interpret waver of the billet as it emerges from the mold as a defect in the product when in fact no product defect exists.
Other proposals have involved the use of a sensing lever on one side of a billet to detect its position or deflection during processing. Such systems, likewise, do not affirmatively sense changes in cross-sectional dimensions of the strand.
Another proposal involves the use of a mechanical, electrical or optical ingot thickness sensor for a steel billet coming off a casting line. In response to sensed thickness, various characteristics of the casting process can be altered, in order to maintain the desired thickness. Again, no direct indication of diagonal deformation results.
In other applications, it has been suggested to use substantially immovable force sensors impinging on surfaces of cast steel product to measure its characteristics. Still other proposals, directed more specifically toward rectangular billets, involve substantially immovable rollers for engaging the edges of the strand to squeeze it during production to maintain a desired cross-sectional configuration. This means, however, sometimes causes cracking or other imperfections in the product, rather than minimizing or eliminating them.
In addition to the on-line techniques described above, diagonal dimension of rectangular cross-sectioned billets has been manually measured by means such as calipers after production and cutting. While this technique detects product distortion imperfection, it does not furnish such information sufficiently early to enable remedial measures in the production operation which would otherwise minimize or eliminate product defects.
It is thus a general object of this invention to produce on-line an unambiguous real time direct measurement indication of cross-sectional diagonal distortion of a cast product strand without influencing product characteristics by the automatic measurement operation itself.